Degradation of the DC current capability in long-emitter bipolar transistors

The degradation of current capability in high speed bipolar transistors caused by the voltage drop across the distributed resistance of the emitter finger has been studied. Experimental results show that in very-long emitter transistors this phenomenon becomes tangible even at current levels well below the onset of high injection. An analytical model under the assumption of medium current levels has been developed. The comparison between calculated and measured results shows very good agreement.